The invention concerns a method for cleaning the guide rollers of a web printing press comprising a printing material web, guided by a number of guide rollers, and a corresponding device.
Automated cleaning devices have been known for some time for cleaning the cylinders of a web printing press which are directly involved in the printing process, e.g. rubber blanket cylinders and impression cylinders. Such a cleaning device comprises e.g. a brush roller which is moistened with cleaning liquids and introduced in a rotating fashion to the cylinder to be cleaned to dissolve and remove soiling therefrom, such as printing ink residues, loose paper fibers and paper dust.
With today""s conventional printing speeds and increased requirements with regard to printing quality, it is absolutely necessary that those guide rollers which come into contact with the freshly printed printing material web are also regularly cleaned from impurities which accumulate on the guide roller surfaces, in particular, as adhering printing ink residues, paper dust and loose paper fibers, which would otherwise increasingly deteriorate the printing quality.
Since access to the guide rollers is usually difficult and since the number of guide rollers is very large compared to the number of cylinders directly involved in the printing process, it is usually not possible, in practice, to have one conventional automated cleaning device for each guide roller. The guide rollers are therefore conventionally cleaned by hand, with an operator spraying cleaning liquid onto the printing material web and initiating slow movement of the printing material web through the printing machine, wherein he/she manually decelerates a guide roller when the moistened portion of the printing material web moves over this guide roller to thereby generate slippage between the guide roller surface and the printing material web. The cleaning agent supplied, together with the printing material web, to the guide roller surface removes the soiling and the printing material web wipes over the respective guide roller to clean it.
U.S. Pat. No. 4,781,116 discloses a device which automates this long practiced approach for printing machines having paper webs. The system comprises an application device disposed in front of the guide rollers to be cleaned, which removes cleaning liquid from a basin using a dipping roller and applies same to a transfer roller, similar to the printing process, and which in turn contacts the paper web to which the entrained cleaning liquid is transferred. The paper web transports the applied cleaning liquid to the guide rollers to be cleaned, the guide rollers having driving motors which are coupled to the corresponding guide roller for generating a slippage between the paper web and the guide roller surface. This prior art has the associated problem that the transfer roller passes not only cleaning liquid onto the paper web but also impurities, in particular, paper dust, from the paper web back into the cleaning liquid container. This eventually leads to sludge deposits in the cleaning liquid container which have to be removed at regular intervals by hand.
U.S. Pat. No. 5,080,015 discloses a system for cleaning guide rollers of a web printing press based on the same conventional principle, wherein the guide rollers are simply decelerated for producing the required slippage and the cleaning liquid is applied to the paper web using spraying nozzles. The spraying nozzles eliminate the above-mentioned disadvantage of prior art according to U.S. Pat. No. 4,781,116 but there are still problems: Spraying always produces some atomization which causes undesirable operation risks. The risk to the workers breathing in the vapor is only one aspect. The cleaning liquids used e.g. for printing papers usually contain an oily component and thus the atomization precipitation on stairs and scaffoldings causes serious problems with respect to working safety. A further problem consists in spraying the optimum amount of cleaning liquids for each kind of paper web, the quality of which can rapidly change. Excessive cleaning liquid causes dripping. Too little cleaning liquid produces unsatisfactory cleaning results.
Departing from the above mentioned prior art, it is the underlying purpose of the invention to propose a method and a corresponding device, on the basis of the described principle, for cleaning the guide rollers of a web printing press which ensures reliable, safe, low-maintenance, automated cleaning of the guide rollers.
This object is achieved by a method and device comprising the features of the accompanying independent claims. Advantages further developments of the method and device can be extracted from the dependent claims.
The inventive method and the corresponding device are based on the known principle of applying cleaning liquid onto the printing material web and transporting it, using the printing material web, to the guide rollers to be cleaned, wherein the guide rollers to be cleaned are decelerated or accelerated while the printing material web is running to generate slippage between the printing material web and the surface of the respective guide roller such that soiling of the guide roller surface is wiped off and removed by the printing material web which is either charged with cleaning liquid and/or is dry. Depending on the printing material used, an optimum cleaning result can be achieved when slippage between the guide roller and the printing material web is produced while the moistened web contacts the guide roller. It may also be advantageous to move the moistened web over the guide rollers without slippage such that the printing ink residues adhering thereto are dissolved and the dissolved soiling is wiped off with a subsequent dry portion of the printing material web, i.e. slippage is produced only when the moistened web portion terminates.
In accordance with the invention, the cleaning liquid is neither applied to the printing material web using a transfer roller nor with spraying nozzles. For application of cleaning liquid, the printing material web is guided along a container holding cleaning liquid in such a fashion that it comes into direct contact with the cleaning liquid held in the container to thereby accept the cleaning liquid.
In accordance with the invention, optimum application of cleaning liquid onto the printing material web is achieved when the web accepts the cleaning liquid itself by soaking up the cleaning liquidxe2x80x94depending on the type of printing material web usedxe2x80x94or by accepting a liquid film adhering to its surface due to adhesion forces and surface tension effects. The charging of the printing material web with cleaning liquid thus adapts automatically to the maximum or nearly maximum absorption capacity of the printing material web, without requiring any regulating measures. When the printing material is changed, no changes are required in the application of the cleaning liquid. At the same time, the surroundings of the application device are not influenced by the application of the cleaning liquid, in particular there is no disadvantageous atomization. Soiling of the stored cleaning liquid in the container is also unlikely since the printing material web only accepts cleaning liquid and the cleaning liquid does not flow back into the container. Finally, the application, in accordance with the invention, of liquid onto the printing material web is not negatively effected when printing material webs of different widths are used in the same machine. For application of liquid according to prior art, in particular using spraying nozzles, e.g. half of the spraying nozzles must be switched off when working with a printing material web which is only half as wide. This switching off must be coupled with information concerning which xe2x80x9chalfxe2x80x9d of the printing material web is to be covered. In contrast thereto, in accordance with the invention, liquid is applied only when a printing material web is present. Application of liquid in accordance with the invention is therefore completely independent of the width and position of the printing material web.
There are various concrete embodiments of the invention. The printing material web may e.g. be dipped into the cleaning liquid contained in the container or guide along its surface. In the simplest case, the container is a basin with an open top. In a particularly preferred manner in accordance with the invention, the cleaning liquid is guided to the printing material web via an elastically deformable sealing lip disposed on the container. A sealing lip of this kind may be disposed, in particular, on the side of the container with the level of the cleaning liquid being slightly above the outer edge of the sealing lip. When the printing material web is guided past the sealing lip, it then accepts the liquid above the sealing lip under laminar flow thereof. The sealing lip thereby ensures that the cleaning liquid reaches the web without leaking.
In all these cases one must ensure that the level of the cleaning liquid in the container is held constant within close tolerances and independent of the amount of cleaning liquid removed by the printing material web. This is preferably achieved in that the container is provided with an overflow and simultaneously supplied with more cleaning liquid than can be removed by the printing material web. A dynamic balance is thereby generated which keeps the level constant within very close tolerances without having to provide sensors for level measurement and separate control circuits.
The cleaning liquid flowing out of the container via the overflow is preferably collected in a collector and the container is directly supplied with cleaning liquid from this collector to thereby form a circuit for the cleaning liquid from which cleaning liquid is only removed by the printing material web. The amount of cleaning liquid removed is added to this circuit e.g. from a supply tank with the collector preferably serving as a buffer.
The advantageously provided sealing lip is preferably adjusted at an acute angle with respect to the printing material web such that the cleaning liquid volume present above the sealing lip is reduced towards the outer edge provided for contact with the printing material web. This is advantageous with regard to possible spilling of the cleaning liquid. In addition, the printing material web abuts in a very flat manner on the sealing lip to greatly reduce the risk of web breakage.
The cleaning liquid container in accordance with the invention must be removed from the printing material web during normal operation of the printing machine to prevent disturbance of the printing process. Conversely, the container must address the printing material web for carrying out the inventive method. To keep the number of mechanical parts as small as possible, and mainly to minimize the space requirements of the container, advancement and withdrawal of a container comprising a sealing lip is preferably effected by pivoting the container about an axis extending parallel to the printing material web. For advancing the sealing lip to the printing material web, the container is tilted towards same. For termination of liquid application it is tilted away from same. This is not only efficient and space-saving but also permits, in particular, very rapid interruption of liquid application.
A pivotable container comprising a sealing lip of this kind is preferably dimensioned such that the cleaning liquid is safely below the outer edge of the sealing lip in the withdrawn position. When the container is pivoted towards the printing material web and the sealing lip contacts the printing material web, the level of the cleaning liquid is close to but not above the outer edge of the sealing lip. Further pivoting of the container towards the printing material web (which is possible due to the elastic deformability of the sealing lip) causes the level of the cleaning liquid to move above the edge of the sealing lip and the cleaning liquid comes into direct contact with the printing material web to be entrained thereby for passage to the guide rollers. When the sealing lip is withdrawn from the printing material web, the reverse effect is achieved. This geometry ensures that no cleaning liquid is spilledxe2x80x94even in event of an emergency switch-off.
With an optional overflow for keeping the liquid level on the side of the container opposite to the sealing lip constant, the edge of the overflow rises, as does the level of the cleaning liquid in the container, as soon as the container is pivoted towards the printing material web. This enhances the effect described above in a particularly simple fashion when the geometry has been appropriately selected. For fine adjustment purposes, the overflow may be designed in a height-adjustable or height-controllable fashion.
Further advantage can be achieved when the pivotable container is integrated in a stationary casing such that when the container is pivoted back, the sealing lip abuts an upper delimitation of the casing to close same. This ensures that the cleaning liquid, which usually has a low vapor pressure, does not evaporate during operation of the printing machine. Conversely, dust or similar soiling cannot gain access to the container during operation.
For reasons of safety, a collecting lip may be disposed below the sealing lip which contacts the printing material web at the same time or somewhat earlier than the sealing lip and which is connected to the collector. Cleaning liquid dripping from the sealing lip is then collected by the collecting lip and guided back into the collector, i.e. back into the circuit.
Should a casing be provided which is to be closed when the container has been pivoted back, the collecting lip may be formed such that, when the container has been pivoted, it abuts, at one side, against a lower delimitation of the casing and, on its other side, against the sealing lip to thereby close the casing. The casing thus includes not only the container with its sealing lip but also the collector for the cleaning liquid.
To limit application of cleaning liquid onto the printing material web to amounts below a maximum possible reception amount of the printing material web, a sealing lip having a toothed edge may be used. When the sealing lip contacts the printing material web, it yields in its direction of motion due to its elastic deformability, i.e. deforms. The individual teeth of a toothed edge of the sealing lip act as obstacles for the cleaning liquid such that same can gain access to the printing material web only at the intermediate spaces between the teeth. Depending on the ratio between the width of the teeth and the width of the tooth gaps, the resulting partial application of cleaning liquid to be printing material web delimits application of the cleaning liquid. The toothing may thereby have different shapes, e.g. comprising triangular or rectangular teeth and also rounded or wavy teeth.
A further particularly advantageous possibility to delimit application of cleaning liquid below a maximum possible amount which the printing material web can receive, consists in a cycled operation of the application device. When application of liquid onto the printing material web is activated and deactivated in rapid succession, the average amount of applied liquid amount can be adjustedxe2x80x94depending on the cycle times and intervals. This has the particular advantage that, in contrast to the toothed sealing lip, the structure of the application device must not be changed. Appropriate cycle control is sufficient. The cycling is particularly easy to carry out using a pivotable container comprising a sealing lip. In this event, a slight cycled tilting motion of the container is sufficient to achieve the desired liquid application effect. Tests with such an application device have shown that a cycle frequency on the order of 1 Hz generates liquid moistened strips of a few centimeters in length on a paper web for newspaper roller offset printing which alternate with associated dry web portions. The average amount of cleaning liquid transferred about the surface circumference of the guide roller to be cleaned can thus be accurately controlled.
The sealing lip may form at least part of the container wall facing the printing material web, wherein the container end face is provided with elastically deformable or foldable walls to seal the end faces of the container.
Supply of cleaning liquid into the container is preferably effected simultaneously at different locations distributed about its volume to avoid formation of turbulences within the container and decreases in or sloping of the cleaner level. Moreover, the cleaning liquid is preferably supplied from below the normal level to prevent impairment of the surface of the liquid and to avoid the formation of waves. This is achieved in a most simple fashion by disposing a duct element, having radial openings, within the container. This may be e.g. a pipe or tube comprising a plurality of bores distributed along its length.
To apply cleaning liquid to the printing material web from both sides, the application device may comprise two containers disposed on both sides of the printing material web. It is thereby particularly advantageous if the two containers are disposed facing one another since the two sealing lips mutually exert the required reaction force. If the reaction force must be produced by the web tension alone, the adjustment force of the sealing lip is poorly defined and the danger of web breakage is considerably increased.
Concrete embodiments of the invention are described and explained in more detail below with reference to the enclosed drawing.